Optical disk apparatus for accessing optical disks with different substrate thicknesses

Abstract

An optical disk apparatus is described which can read information from and write information to optical disk of different thicknesses. The optical disk apparatus includes coupling lenses which alter the focusing capabilities of an objective lens which controls reading and writing to the optical disk. Thus, the present invention allows both "standard density" and "high density" optical disks to be accessed by the same optical disk apparatus.

What is claimed is: 
     
       1. An optical disk apparatus comprising: a laser generator for radiating laser rays for reading information from and writing, information to optical disks with different substrate thicknesses, said laser generator including a first laser source and a second laser source whose axes are at right angles to each other;   an objective lens for focusing the laser rays from the laser generator and forming a laser spot on a recording layer of the optical disk;   at least one photo detector for receiving reflective light from the optical disk and for outputting a reproducing signal and servo signals;   a beam splitter located in an optical path between the first laser source and the second laser source; and,   at least one coupling lens located either in an optical path between the beam splitter and the first laser source, or in an optical path between the beam splitter and the second laser source, the coupling lens allowing the objective lens to focus on optical disks of different substrate thickness without causing a spherical surface aberration; and   wherein the at least one photo detector further comprises: a first photo detector element for receiving a laser ray radiated from the first laser source and reflected from the optical disk;   a second photo detector element for receiving a laser ray radiated from the second laser source and reflected from the optical disk; and,   a judging control circuit for judging substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and for connecting either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit.     
     
     
       2. An optical disk apparatus comprising: a laser generator for radiating laser rays for reading information from and writing information to optical disks with different substrate thicknesses, said laser generator including a first laser source and a second laser source whose axes are at right angles to each other;   an objective lens for focusing the laser rays from the laser generator and forming a laser spot on a recording layer of the optical disk;   at least one photo detector for receiving reflective light from the optical disk and for outputting a reproducing signal and servo signals;   a beam splitter located in an optical path between the first laser source and the second laser source; and,   at least one coupling lens located either in an optical path between the beam splitter and the first laser source, or in an optical path between the beam splitter and the second laser source, the coupling lens allowing the objective lens to focus on optical disks of different substrate thickness without causing a spherical surface aberration,   wherein the lengths of the optical paths from the first laser source and the second laser source to the beam splitter are adjusted, so that the objective lens can be focused on a recording layer of the optical disk without causing a spherical surface aberration; and,   wherein the at least one photo detector further comprises: a first photo detector element for receiving a laser ray radiated from the first laser source and reflected from the optical disk;   a second photo detector element for receiving a laser ray radiated from the second laser source and reflected from the optical disk; and,   a judging control circuit for judging substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and for connecting either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit.     
     
     
       3. The optical disk apparatus of claim 1, wherein laser rays radiated from one of the first laser source and the second laser source are P polarizing light rays, and laser rays radiated from the other are S polarizing light rays. 
     
     
       4. The optical disk apparatus of claim 2, wherein laser rays radiated from one of the first laser source and the second laser source are P polarizing light rays, and laser rays radiated from the other are S polarizing light rays. 
     
     
       5. The optical disk apparatus of claims 1, further comprising: a λ/2 plate for changing the polarizing direction of a laser ray passing through the optical path either between the first laser source and the beam splitter or passing through the optical path between the second laser source and the beam splitter,   wherein the polarizing direction of the ray passing through said λ/2 plate is changed by 90 degrees.   
     
     
       6. The optical disk apparatus of claims 2, further comprising: a λ/2 plate for changing the polarizing direction of a laser ray passing through the optical path either between the first laser source and the beam splitter or passing through the optical path between the second laser source and the beam splitter,   wherein the polarizing direction of the ray passing through said λ/2 plate is changed by 90 degrees.   
     
     
       7. The optical disk apparatus of claim 1, further comprising: a power monitor for detecting the power of laser rays radiated from both the first laser source and the second laser source.   
     
     
       8. The optical disk apparatus of claim 2, further comprising: a power monitor for detecting the power of laser rays radiated from both the first laser source and the second laser source.   
     
     
       9. The optical disk apparatus of claim 1, further comprising: a half mirror located between the objective lens and beam splitters, for reflecting the laser ray reflected from the optical disk,   wherein the at least one photo detector receives the laser ray reflected by the half mirror and outputs a reproducing signal and servo signals.   
     
     
       10. The optical disk apparatus of claim 2, further comprising: a half mirror located between the objective lens and beam splitters, for reflecting the laser ray reflected from the optical disk,   wherein the at least one photo detector receives the laser ray reflected by the half mirror and outputs a reproducing signal and servo signals.   
     
     
       11. An optical disk apparatus for reading information from and writing information to optical disks with different substrate thicknesses, comprising: a first photo detector element for receiving a laser ray radiated from a first laser source and reflected from an optical disk;   a second photo detector element for receiving a laser ray radiated from a second laser source and reflected from the optical disk; and,   a judging control circuit for judging substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and for connecting either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit.   
     
     
       12. An optical disk apparatus for reading information from and writing information to optical disks with different substrate thicknesses, comprising: a first photo detector element for receiving a laser ray radiated from a first laser source and reflected from an optical disk;   a second photo detector element for receiving a laser ray radiated from a second laser source and reflected from the optical disk; and,   a judging control circuit for judging substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and for connecting either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit;   wherein the lengths of the optical paths from the first laser source and the second laser source to a beam splitter are adjusted so that an objective lens can be focused on a recording layer of the optical disk without causing a spherical surface aberration.   
     
     
       13. A method of accessing a recording layer of an optical disk comprising the steps of: providing first and second laser sources located in first and second perpendicular optical paths; providing a beam splitter located at the intersection of the first and second optical paths;   providing at least one coupling lens in either the first or second optical path which reduces a spherical surface aberration;   providing an objective lens which focuses a laser ray emitted from said beam splitter on a recording layer of an optical disk;   providing a first photo detector element for receiving a laser ray radiated from the first laser source and reflected from the optical disk;   providing a second photo detector element for receiving a laser ray radiated from the second laser source and reflected from the optical disk;   providing a judging control circuit which judges a substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and which connects either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit; and,   reading or writing information to the recording layer of the optical disk through the focused laser ray.   
     
     
       14. The method of claim 13, wherein the lengths of the optical paths from the first laser source and the second laser source to the beam splitters are adjusted, in order to reduce a spherical surface aberration. 
     
     
       15. The method of claim 13, further comprising the step of: providing a λ/2 plate for changing the polarization direction of a laser ray radiated from one of the first or second laser sources by 90 degrees.   
     
     
       16. The method of claim 13, wherein one of the laser sources provides a P polarized light ray and the other provides an S polarized light ray. 
     
     
       17. The method of claim 13, further comprising the step of: providing a power monitor for detecting power of laser rays radiated from both the first laser source and the second laser source.   
     
     
       18. The method of claim 13, further comprising the step of: providing a half mirror located in an optical path between the objective lens and beam splitter, for further reflecting a laser ray reflected from the optical disk; and   providing at least one photo detector,   wherein the at least one photo detector receives the laser ray reflected on the half mirror and outputs a reproducing signal and servo signals.   
     
     
       19. A method of accessing a recording layer of an optical disk comprising the steps of: providing a first photo detector element for receiving a laser ray radiated from a first laser source and reflected from the optical disk;   providing a second photo detector element for receiving a laser ray radiated from a second laser source and reflected from the optical disk;   providing a judging control circuit which judges a substrate thickness of the optical disk based on signals from the first photo detector element and the second photo detector element, and which connects either the first photo detector or the second photo detector with a power source in accordance with an output from said judging control circuit; and,   reading or writing information to the recording layer of the optical disk through a focused laser ray.